In the treatment of tumors by radiation therapy, the radiation is often delivered in small doses over many sessions (or fractions). One reason this is done, is to allow the surrounding healthy tissue to tolerate the total radiation dose. Delivering the total dose in many fractions also smoothes out any patient positioning errors which may occur.
The advent of modern computer controlled Radiation Therapy machines such as linear accelerators allows higher doses to be delivered in fewer fractions (often referred to as hypo-fractionation). This kind of treatment regime can be popular with patients due to the reduced time required of the patient for treatment. It can also reduce the cost of healthcare as the treatment times are shorter. However, these kinds of treatment require higher patient positioning accuracy. In addition, due to the need to limit the dose to the healthy tissue, it is desirable to be able to treat with a maximum of beam paths which enter the patient from many directions. This can be accomplished on a modern linear accelerator through the use of VMAT techniques and non-coplanar beam angles. Traditional linear accelerators generally treat in planes which are perpendicular to the patient axis. Through the use of modern computer controls, it is possible to treat in planes that are not perpendicular (coplanar) to the patient axis.
This new capability can be enhanced and enabled through the use of well designed positioning devices. In the present invention, we have developed the ability to allow greater access to the torso so that treatments can be delivered, unimpeded by the positioning devices themselves. This is particularly beneficial in Proton Therapy since the negative impact of treating through the device is even greater than with standard linear accelerator techniques.